What it does: Zinc lozenges "can shorten the duration of the common cold" when taken early into infection, Dr. Mafi said, though he noted some uncertainty in the data. Other doctors have pointed out that you should be careful taking zinc due to its potential side effects (which can include nausea, especially when taken on an empty stomach, and diarrhoea) and avoid zinc intranasal sprays, which can cause irreversible loss of smell. When taken properly, though, zinc does support immune health: when a pathogen enters your bloodstream, zinc enters the affected cell and stops the infection from escalating at its normal rate and putting a strain on your immune system.
Where to find it: Great sources of zinc are varied and include spinach, beef, prawns, kidney beans, and flax seeds. Most immune-related studies on zinc focus on syrups and lozenges.